A lone armed man with reported mental-health issues carried out Monday's attack at Washington DC's Navy Yard, killing 12 people and injuring eight, US authorities say.
The US Defence Department said on Tuesday that it was reviewing security measures at all of its bases following the attack.
According to police, military contractor Aaron Alexis, 34, of Texas, launched the attack on Monday inside a building at the navy complex, shooting people in a cafeteria and hallway. He was eventually shot by police.
Alexis carried two weapons in the attack: a shotgun and a handgun that he took from a police officer at the scene. The FBI said he was not carrying an AR-15 rifle, contradicting previous reports.
Cathy Lanier, Washington's police chief, said no one else was involved in the attack.
Al Jazeera's Kimberly Halkett, reporting from Washington DC on Tuesday, said: "A picture is emerging of someone with a very troubled past and a history of anger-management issues.
"He had been treated for mental health issues, including sleeping disorders and paranoia."
Alexis also served as a navy reservist from 2007 to early 2011 before being discharged.
He held the rank of an aviation electrician's mate 3rd class and had served full-time in a logistics support squadron in Forth Worth, according to the US Navy.
Police in Seattle said Alexis was arrested there in 2004 for shooting the tyres of another man's car in what he described to detectives as an anger-fuelled "blackout''.
The FBI said Alexis used a valid pass to get on the Washington base, where 18,000 people work. He was serving as an employee of an IT company called The Experts, a subcontractor for Hewlett-Packard.
In a statement, The Experts said that Alexis had been employed for six months and two background checks were performed on his character, the last being in June which revealed no issues other than one minor traffic violation.
President Barack Obama mourned what he called "yet another mass shooting'' in the US. The Senate was closed, a baseball game postponed and a White House celebration delayed following the shooting.
"It's a shooting that targeted our military and civilian personnel," Obama said.
"They were patriots and they know the dangers of serving abroad, but today they face the unimaginable violence that they wouldn't have expected here at home."
Source: Al Jazeera and agencies